1. Field of the Invention
The present invention is directed, in general, to high-pressure fluid systems, and in particular to high-pressure fittings for such systems, such as elbows, tees, and crosses.
2. Description of the Related Art
High-pressure fluid systems are used in many industrial applications. For example, a high-pressure pump may be used to provide a pressurized stream of water for cleaning and surface preparation of a wide variety of objects, such as machine parts and ship hulls. High-pressure fluid systems are also used to provide a pressurized stream of water for waterjet and abrasive waterjet cutting. Another use for such systems is in the operation of isostatic pressurization. In such an application, other fluids or objects are subjected to extremely high isostatic pressure for the purpose of sterilizing food products, forming mechanical parts, hardening machine parts, etc.
Applications of the kinds described above may employ fluid systems operating at fluid pressures in a range of 30,000-100,000 psi. Given the immense pressure in such systems, one of the greatest challenges is the transmission of pressurized fluid from one or more fluid pumps to the tools or devices that employ the high-pressure fluid.
FIG. 1 is a horizontal cross section (see lines 1-1 of FIG. 2) of a typical high-pressure fitting, according to known art. FIG. 2 shows the fitting 100 taken along lines 2-2 of FIG. 1. The fitting 100 includes a body 102 with a plurality of threaded apertures 112, to which high-pressure fluid transmission lines 106 are coupled via collars 103 and glands 104. Conical terminations 107 of the fluid transmission lines 106 are biased against conical coupling seats 105 of the body 102 by the threaded glands 104, and thereby form a fluid seal. Weep holes 111 are configured to vent fluid from the apertures 112 to prevent pressurization of the threaded coupling in the event that a seal between a termination 107 and seat 105 fails. It may be seen that X and Y fluid channels 108, 110 meet and cross in the center of the body 102.
The cross-fitting of FIGS. 1 and 2 may be used to collect or distribute fluid, or both, as required. For example, in a case where a single fluid pump is not capable of providing sufficient pressurized fluid for a given application, a second, and even a third pump may be coupled to the cross-fitting 102 at respective ones of the apertures 112, while the remaining aperture 112 is employed to provide pressurized fluid to the selected application, such as an isostatic press or waterjet cutting system. In another case, a single fluid pump may be used to provide pressurized fluid to a plurality of tools, in which case the pump is coupled to a first aperture 112, while each of the plurality of tools is coupled to a further one of the apertures 112.
While a cross-fitting has been described with reference to FIGS. 1 and 2, it will be understood that a T-fitting and an elbow-fitting each function in a similar manner, with the exception that, in the case of a T-fitting, the fitting will have a first fluid channel such as channel 108 pictured in FIG. 2, that traverses the fitting, and a second fluid channel such as the channel 110 of FIG. 2, but which only penetrates from an aperture far enough to join with the first fluid channel, without traversing the body of the fitting. In the case of an elbow-fitting, of course, first and second fluid channels each terminate at a central region of the fitting, without traversing the fitting. The elbow-fitting, in particular, may have channels intersecting at angles other than 90 degrees, while such variations of angle are less common in tee and cross-fittings.
Due to the tremendous pressures transmitted through such fittings, the fittings must be manufactured using extremely strong materials. Nevertheless, fittings such as that described with reference to FIGS. 1 and 2 are commonly subject to failure. In fact, failures of such fittings are one of the most frequent causes of down time and repair expense in high-pressure fluid systems.
When a high-pressure fluid fitting of the type described with reference to FIGS. 1 and 2 is subjected to extreme fluid pressures, fluid within the X channel 108 exerts internal separation forces on the body 102 of the fitting 100 along vectors that are parallel to a Y-Z plane, while fluid in the Y channel exerts separation forces on the body 102 along vectors that are parallel to an X-Z plane. Thus, the fitting 100 is subject to separation forces on vectors that are parallel to a Z axis in magnitudes that are twice as great as in any other direction. Furthermore, because of the sharp corners in the X and Y channels 108, 110 where they intersect, separation forces are concentrated there, and crack initiation is most common at these corners. FIG. 2 shows cracks 116 forming at the point where fluid channels 108, 110 intersect in the middle of the body 102.
Because of the comparatively greater Z axis separation forces, cracks tend to propagate horizontally, i.e., substantially parallel to an X-Y plane, in the body of the fitting. As a horizontal crack appears, the surface area within the crack is subjected to further separation forces parallel to the Z axis, without significant increase in forces in any other direction. Accordingly, once initiated, a crack very quickly propagates, and may eventually destroy the fitting.